If these weak passive guys are letting you get away with controlling the pot, great. Just set yourself some good odds, and make some blocking bets. This confuses the fuck out of most standard weak tighties, they don't know what else to do but to call.
As for firing the river if you miss, I peronally don't unless I think THEY missed their draw. I have no problem in check folding if I miss, like they pay attention at our levels anyways?